Solid composite propellants containing copolymers of conjugated dienes with unsaturated carboxylic acids

ABSTRACT

1. A solid propellant composition comprising an inorganic oxidizing salt and a synthetic polymeric binder formed by reacting a first uncured liquid polymer of conjugated dienes having four to 12 carbon atoms per molecule, said first polymer containing at least about two acidic groups per molecule with a polyfunctional organic compound containing at least 3 functional groups reactive with said acidic groups and selected from the group consisting of aliphatic polyepoxides, polyaziridinyl triazines, polyaziridinyl triphosphatriazines, triaziridinyl phosphine oxides, and triaziridinyl phosphine sulfides, said binder containing a plasticizing amount of a second liquid polymer of 1,3-butadine having its unsaturation in the form of vinyl content in the range of 0 to 25 per cent, trans content in the range of 0 to 60 per cent, and cis content in the range of 30 to 85 per cent, and a viscosity in the range of 10 to 500 poises at 77* F.

flied tates Patent 1 Zelinski et al.

[ SOLID COMPOSITE PROPELLANTS CONTAINING COPOLYMERS OF CONJUGATED DIENES WITH UNSATURATED CARBOXYLIC ACIDS [75] Inventors: Robert P. Zelinski; Paul S. Hudson,

both of Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

[22] Filed: May 15, 1961 [21] Appl. No.: 110,617

[52] US. Cl 149/199, 149/191, 149/1991, 149/20, 149/196, 149/195 [51] Int. Cl C06d 5/06 [58] Field of Search 149/17, 18, 19, 20, 60, 149/83 Primary Examiner-Benjamin R. Padgett EXElVHLARY CLAIM l. A solid propellant composition comprising an inorganic oxidizing salt and a synthetic polymeric binder formed by reacting a first uncured liquid polymer of conjugated dienes having four to 12 carbon atoms per molecule, said first polymer containing at least about two acidic groups per molecule with a polyfunctional organic compound containing at least 3 functional groups reactive with said acidic groups and selected from the group consisting of aliphatic polyepoxides, polyaziridinyl triazines, polyaziridinyl triphosphatriazines, triaziridinyl phosphine oxides, and triaziridinyl phosphine sulfides, said binder containing a plasticizing amount of a second liquid polymer of 1,3-butadine having its unsaturation in the form of vinyl content in the range of 0 to 25 per cent, trans content in the range of 0 to 60 per cent, and cis content in the range of 30 to 85 per cent, and a viscosity in the range of 10 to 500 poises at 77 F.

12 Claims, N0 Drawings 1 SOLlD COMPOSITE PROPELLANTS CONTAINING COPOLYMERS F CONJUGATED DHENES WITH UNSATURATED CARBOXYLIC ACIDS This invention relates to improved solid propellants. In another aspect it relates to a method of preparing a composite propellant containing inorganic oxidizing agent and rubbery binder which has improved properties at low temperatures.

In the past fifteen years or so, great interest has developed in solid propellants for jet propulsion devices such as missiles, rocket motors, gas generators, and the like. One type of solid propellant which has received considerable attention is that of the composite type, a typical composite propellant being one that uses an organic material as the fuel and binder, and a solid oxidant such as ammonium nitrate. In this type of propellant particularly when the propellant comprises a major proportion of a crystalline oxidizer and a minor proportion of the fuel and binder, the problem is presented of adjusting the physical properties of the propellant because of the small proportion of the binder material. Thus, it is difficult to provide suitable adhesion to the particles of oxidizer and the matrix of binder material is so tenuous that it is difficult to provide sufficient strength and elasticity in the propellant structure. Also, in many cases it is desirable and necessary to be able to cast or pour the propellant into a rocket case or mold and then cure to a solid having suitable properties. In addition, since the binder also forms a fuel or part of the fuel it must have suitable chemical properties for this purpose.

It has been disclosed in the copending application of P. S. Hudson and C. C. Bice, Ser. No. 829,462, filed July 24, 1959, now US. Pat No. 3,087,844 that an im proved binder for a composite solid propellant can be provided from a synthetic polymer or copolymer containing terminal acidic groups or a synthetic copolymer of an unsaturated carboxylic acid which has been reacted with a tri(aziridinyl)-phosphine oxide or a tri(a2iridinyl)phosphine sulfide. In a preferred method of manufacturing a solid propellant grain the uncured propellant composition is poured into a case or mold as a fluid mass and subsequently cured to a resilient solid. The binder in such a casting operation must be quite fluid prior to curing and a high degree of cure is required in order to convert the polymer which is fluid to a solid with acceptable strength. Cured propellant grains must have sufficient mechanical strength to withstand the stress of handling and enormous thrusts encountered in use, as well as resiliency to resist cracking. These properties must be acceptable over a very wide range of temperature and for long periods of time.

We have discovered a method of facilitating the fabrication of solid propellant compositions while at the same time improving the properties of the cured propellant at extremely low temperatures, for example, 40 to 90 F. According to our invention propellant compositions which include substantial amounts of inorganic oxidizing salt and a synthetic polymeric binder which contains at least about 2 acidic groups per mole cule and is cured by reacting the acidic groups with a polyfunctional curing agent are plasticized with a polymer of butadiene having a vinyl content in the range of 0 to 25 per cent, a trans content in the range of 0 to 60 per cent and a cis content in the range of 30 to 85 per cent, and a viscosity in the range of 10 to 500 poises at 77 F. By using this type of plasticizer the propellant compositions are made substantially more fluid to facilitate casting operations and/or permit the use of substantially higher amounts of solid oxidant. The use of the plasticizer according to our invention enables the fabricator to control the fluidity of the uncured propellant composition while at the same time obtaining a cured propellant grain which has substantially improved elongation properties at low temperatures. As a result of these improved elongation properties the propellant grain is able to withstand considerably more stress and shock without rupturing or altering the burning characteristics of the grain.

It is an object of our invention to provide an improved solid propellant. Another object of our invention is to provide a method of preparing a composite propellant including inorganic oxidizing salt and rubbery'binder which has been plasticized to improve the fluidity of the uncured propellant composition. Another object is to provide a method for preparing a propellant with substantially improved elongation properties at low temperatures. Another object of our invention is to provide a method of plasticizing an uncured propellant composition to facilitate casting operations or incorporation of larger amounts of inorganic oxidizing salt while at the same time improving the low temperature elongation of the cured propellant. Other objects, advantages, and features of our invention will be apparent to those skilled in the art from the following discussion.

The solid propellants which are modified according to our invention comprise an inorganic oxidizing salt and a synthetic polymeric binder. The binder is formed by reacting a first uncured conjugated diene liquid polymer containing at least about two acidic groups per molecule with a polyfunctional organic compound that will react with the acidic groups present in the diene polymer. The binder also contains, according to our invention, a plasticizing amount of a second 1,3- butadiene polymer having its unsaturation in the form of vinyl content in the range of 0 to 25 per cent, trans content in the range of 0 to 60 per cent, and cis content in the range of 30 to per cent and a viscosity in the range of 10 to 500 poises at 77 F. A number of different inorganic oxidizing salts can be employed and generally these materials are well known in the art. Typical of such salts are the ammonium, alkali metal, and alkaline earth metal salts of nitric, perchloric and chloric acids, and admixtures thereof, such as sodium perchlorate, potassium perchlorate, magnesium perchlorate, ammonium perchlorate, potassium nitrate, sodium nitrate, calcium nitrate, ammonium nitrate and the like.

The conjugated diene polymers which are used to form the binder of the propellant can be either a homopolymer of a conjugated diene, copolymers of more than 1 conjugated diene or copolymers of conjugated dienes with other copolymerizable materials. In such copolymers the conjugated dienes should comprise a major amount of the incorporated monomer in the polymer. Conjugated dienes contain ordinarily from four to 12 carbon atoms per molecule and those containing four to eight carbon atoms such as 1,3- butadiene, isoprene, piperylene, methylpentadiene, propylbutadiene, 1,3-octadiene and the like are preferred. Conjugated dienes can contain reactive substituents along the chain such as, for example, halogenated dienes of which chloroprene and fluoroprene are typical. Butadiene is preferred with isoprene and piperylene also being especially suitable. The copolymerizable monomers include those containing a group such as the vinyl substituted aromatic compounds. The vinyl-substituted aromatics include styrene l-vinylnaphthalene, 2-vinylnaphthalene, and alkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkoxy, araloxy and dialkylamino derivatives thereof in which the total number of carbon atoms in the combined substituents does not exceed 12. Examples of these aromatic monomers include 3-methylstyrene(3-vinyltoluene), 4-npropylstyrene, 4-dodecylstyrene, 4-cyclohexylstyrene,

4-phenylstyrene, 2-ethyl-4-benzylstyrene, 4-ptolylstyrene 4-( 4-phenyl-n-butyl )styrene, 4- methoxystyrene, 3 ,5 diphenoxystyrene, 4- dimethylaminostyrene, 4-methoxy-6-di-npropylaminostyrene, 4,5-dimethyll vinylnaphthalene, 8-phenyll -vinylnaphthalene, 4-methoxyl vinylnaphthalene, 3 ,6-dimethylaminol vinylnapthalene, and the like. Block or random copolymers of conjugated dienes and vinyl-substituted aromatic compounds can be formed. Block copolymers can also be prepared between conjugated dienes and polar monomers which are introduced after the conjugated diene has polymerized. These polar monomers include vinylpyridines and vinyl-quinolines in which the vinyl group is attached to a ring carbon other than a carbon in the beta position with respect to the nitrogen. These pyridine, quinoline or isoquinoline derivatives can contain substituents such as alkyl, cycloalkyl, aryl alkaryl, aralkyl alkoxy, araloxy and dialkylamino groups in which the total number of carbon atoms in the combined constituents does not exceed 12. Any alkyl groups on the alpha or gamma carbons with respect to the nitrogen should be tertiary alkyl groups. Examples of polar monomers of this type include 2- vinylpyridine, 3,5diethyl-4-vinylpyridine, 3-n-dodecyl- Z-Vinylpyridine, 5cyclohexyl-Z-vinylpyridine, 4-phenyl-2-vinylpyridine, 3-benzyl-4-vinylpyridine, 6-methoxy-2-vinylpyridine, 4-phenoxy-2-vinylpyridine, 4dimethylamino-2-vinylpyridine, 2-vinylquinoline, 3-methyl4-ethoxy-Z-vinylquinoline, 3- vinylisoquinoline, 4-phenyl-l-vinylisoquinoline, and the like.

Other polar monomers include acrylic and alkacrylic acid esters, nitriles, and N,N-disubstituted amides, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, methyl ethacrylate, ethyl ethacrylate, isopropyl ethacrylate, acrylonitrile, methacrylonitrile, N,N-dimethylacrylamide, N,N-diethylmethacrylamide and the like. Vinylfuran and N- vinylcarbazole can also be used.

The above named monomers can be polymerized to form terminally reactive polymers by initiating the polymerization with an organo alkali metal compound containing from two to four or more alkali metal atoms per molecule. Lithium is the preferred alkali metal in these initiators. The organo alkali metal compounds can be prepared in several ways, such as, by replacing halogens in an organic halide with alkali metals, by direct addition of alkali metals to a double bond or by reacting an organic halide with a suitable alkali metal compound. Preparation of the initiator should be carried out in a polar solvent such as diethylether.

The organo alkali metal initiators employed for pre paring the polymers having terminally reactive groups can be represented by the formula RM, where R is the hydrocarbon radical selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, M is an alkali metal including sodium, potassium, lithium, cesium and rubidium, and x is an integer of 2 to 4. The R in the formula generally contains from one to 20 car bon atoms although higher molecular weight compounds can be used. By far the best results are obtained with organo lithium compounds which give very high conversions to the terminally reactive polymer. Examples of poly-alkali metal substituted hydrocarbons of this type include 1,4-dilithiobutane, l,5-dipotassiopentane, 1 ,4-disodio-2-methylbutane, 1 l O-dilithiodecane, 1 ,20-dilithioeicosane, 1,4-dilithio-2-methyl-2butene, l,4-dipotassio-2butene, dilithionaphthalene, 4,4- dilithiobiphenyl, dilithioanthracene, l ,2-dilithiol l diphenylethane, 1 ,2-dilithio-1 ,Z-diphenylethane, l ,4-dilithiocyclohexane, 1 ,3 ,5-trilithiocyclohexane, 1 ,4-dirubidiobutane, l,8-dicesiooctane, l ,5-dilithio-3- pentyne, dilithiophenanthrene, 1,2-dilithiotriphenylethane, dilithiomethane, and the like.

Certain specific initiators give better results than others and are preferred for preparing the polymers. Lithium adducts of naphthalene, methyl naphthalene and anthracene give very good results. A preferred initiator is l,2-dilithio-l,Z-diphenylethane (lithium-stilbene adduct). Other preferred initiators include dilithium adducts of 2,3-dialkyl-1 ,3-butadienes, for example, 2,3-dimethyl-l ,3-butadiene, and especially the dilithium adducts of isoprene and 1,3-butadiene wherein the adduct contains from 1 to 7 diene units per molecule.

In the polymerization using initiators of this type the organo radical of the organo alkali metal compound is incorporated in the polymer chain and the alkali metal atoms are attached terminally to each end of the polymer chain. In general the polymers will be linear having two ends; however, polymers containing more than 2 ends can be prepared. These polymers can be represented by the formula QM where Q comprises the polymer as previously described, M is an alkali metal and n is an integer of 2 to 4.

The polymers which can be improved particularly in low temperature properties according to our invention are the liquid conjugated diene polymers which ordinarily have molecular weights in the range of about 1000 to about 20,000. The molecular weight of the polymer can be controlled by varying the amount of initiator charged to the polymerization reaction. Usually the initiator is used in amounts between about 5 and about millimoles per 100 grams of monomer with the higher amounts of initiator resulting in polymers of lower molecular weight. Ordinarily the amount of initiator does not exceed about 40 millimoles per 100 grams of monomer. The temperature of the polymerization is generally in the range of about l00 to C. and preferably between 75 and +75 C. The temperature used will depend upon the monomers and initiators used in preparing the polymers. The polymerization should be carried out in the presence of a suitable diluent which is predominantly hydrocarbon, such as benzene, toluene, cyclohexane, xylene, n-hexane,

n-heptane, isooctane and the like. In general this diluent is a paraffin, cycloparaffin or aromatic which contains from four to carbon atoms per molecule. Relatively small amounts of other materials can be present, such as ethers in which the initiator was dissolved or a polar compound which is charged to encourage random copolymerization between a conjugated diene and a vinyl-substituted aromatic compound. Ordinarily,

however, it is desired that such polar compounds bemaintained at a minimum in preparing conjugated dienes polymers which have improved low temperature properties.

The polymers which result from the above polymerization contain an alkali metal atom on each end of the polymer molecule and are therefore reactive with various materials which can be used to replace the terminal alkali metal atoms with more stable reactive groups. The polymers employed in the propellants for our invention are reacted to replace the alkali metal atoms with acidic groups such as SOH, SO l-l, SO H, COOl-l, SeO H, SeO l-l, SiO H, S O H, s o u, S OH, SO H TeO l-l, TeO H, AsO l-l, AsOl-l, AsO l-l ASO3H3. Reagents which can be used to form these terminal acidic groups include carbon dioxide, sulfuryl chloride and the like. The resulting polymers are hydrolyzed to remove the alkali metal and replace it with an acidic hydrogen. The reaction of a terminally reactive polymer with the acid-forming reagents can be carried out over a wide temperature range, for example, from 75 to +75 C. Preferably the amount of reagent used to add the acid group is in excess of stoichiometric.

These terminally reactive polymers prepared as described above can be characterized as containing at least about two terminal acidic groups per molecule. While the preponderance of the polymer molecules in the total polymeric composition are polyfunctional, it should be understood that some monoand/or nonfunctional polymer molecules can also be present in small amounts. Minute amounts of moisture in the terminating agent tend to reduce the number of polyfunctional molecules. As an illustration, a polymeric composition in which there is an average of 1.5 to 2.5 terminal acidic groups per molecule can be characterized as a terminally reactive polymer having about two terminal acidic groups per molecule.

Another type of polymer which can be used in the binder of the propellant are copolymers of the conjugated dienes above-named and unsaturated carboxylic acids. The acids which can be used are those containing up to 36 carbon atoms and having from one to five double bonds and one or two carboxy groups per molecule. Also included are the so-called dimerized acids, that is, acids where two molecules of an acid are linked by destroying one of the double bonds. The acids which can be copolymerized with conjugated dienes in this manner include, for example, such acids as acrylic acid, methacrylic acid, itaconic acid, vinylacetic acid, palmitoleic acid, oleic acid, ricinoleic acid, arachidonic acid. erucic acid, selacholeic acid, fumaric acid, maleic acid, and the like. The reaction of the diene and the unsaturated carboxylic acid is carried out over a wide range of temperatures depending upon the monomer and particular acid employed, for example, temperatures between about 50 and about +l00 C. The amount of acid employed in the reaction can vary to provide polymers having acid equivalents from as low as 0.005 to as high as 0.2 equivalents per grams of polymer product. The resulting polymers, however, will contain at least 2 acidic groups per molecule and ordinarily the number of acidic groups will be substantially greater than 2.

The polymers containing acid groups can be cured by reaction with compounds which contain 2 or more functional groups that will react with the acid groups. The most typical and preferred acid group in the binder compositions is the carboxy group. Acidic containing polymers can be cured by reacting them with polyfunctional organic compounds which contain 2 or more aziridinyl groups per molecule. Other polyfunctional compounds which can be used to cure carboxy containing polymers are the aliphatic polyepoxides such as compounds containing 2 or more epoxy groups per molecule. Examples of such compounds are triepoxyhexane, triepoxydecane, 2,3-6,7-1 1 ,12- triepoxydodecane, 2,3-5,6-diepoxy-9-epoxy ethyldodecane, pentaepoxyeicosane, 2,3-5-triepoxy ethyl-9,IO-epoxyhexadecane and the like. In these compounds the per cent epoxy oxygen will usually exceed 0.5 per cent and will preferably be in the range of from 2 to 12 per cent or higher. A particularly useful compound of this class is a liquid epoxidized polybutadiene containing three or more epoxy groups per molecule. These materials which comprise a preferred species can be prepared by treating a liquid polymer of butadiene with a peracid, such as performic or peracetic acid. Rubbery solids can be prepared using from one to 10 equivalents of the epoxy compound based on equivalents of the epoxy groups present per carboxy group equivalent present in the carboxy terminated polymers. The preferred coupling or curing agents are the polyaziridinyl compounds or those containing 2 or more, preferably 3, aziridinyl groups per molecule. Ordinarily when the difunctional aziridinyl compounds are used they are employed in combination with a trifunctional curative. Examples of difunctional compounds include phenyl-bis( 2-methyl-laziridinyl)phosphine sulfide, phenyl-bis(2-methyl-3- ethyl-l-aziridinyl)phosphine sulfide, bis(Z-propyl-laziridinyl)sulfoxide, bis( l-aziridinyl)sulfone, bis( 1,2- propylene)l,3-urea, and the like. Polyfunctional curatives such as the triazines and triphosphatriazines can also be employed in limited amounts. The preferred curatives of the aziridinyl type are the triaziridinyl phosphine oxides or sulfides as represented by the formula:

wherein X is selected from the group consisting of oxygen and sulfur, P is phosphorous, the Rs are radicals containing up to a total of 20 carbon atoms per aziridinyl group, each R being selected from the group consisting of hydrogen, alkyl, cycloalkyl, and aryl radicals and composites thereof such as alkaryl, aralkyl, and the like. Specific phosphine reactants which can be used include tri( l-aziridinyl)phosphine oxide, tri( 2- isopropyl- 1 -aziridinyl )phosphine oxide, tri( 2 ,2- dimethyll -aziridinyl )phosphine oxide, tri( 2-dodecyll-aziridinyl)phsphine oxide, tri( 2-eicosyl-laziridinyl )phosphine oxide, tri( 2-ethyl-3-cyclohexyll aziridinyl)phosphine oxide, tri( 2-phenyl-laziridinyl)phosphine oxide, tri(2-methyl-3-benzyl-- -l-aziridinyl)phosphine oxide, tri[2-n-propyl-3(2- phenylethyl)-l-aziridinyl1phosphine oxide, tri[2- heptyl-3-(2,4-dimethylphenyl)-l-aziridinyl1phosphine oxide, tri( l-aziridinyl)phosphine sulfide, tri(2-methyll-aziridinyl)phosphine sulfide, tri( 2-methyl-3- cyclohexyll -aziridinyl )phosphine sulfide, tri( 2- phenyl-l-aziridinyl)phosphine sulfide, tri(2-amyl-3- benzyl-l-aziridinyl)phosphine sulfide, and the like. Mixtures of tri(Z-methyl-l-aziridinyl)phosphine oxide and phenyl-bis(2-methyl-l-aziridinyl)phosphine oxide are particularly effective.

In preparing the solid propellant the oxidant and the liquid acidic containing polymer are mixed together and this mixture is plasticized by the low vinyl liquid polymer of l,3-butadiene by adding this polymer either before or after incorporating the oxidant. Any method can be employed to prepare this polymer provided the unsaturation is in the form of vinyl content in the range of 0 to 25, preferably 0 to 15 per cent, trans content in the range of 0 to 60, preferably 0 to 55 per cent, and cis content in the range of 30 to 85, preferably 35 to 85 per cent, and the viscosity of the polymer in the range of to 500 poises at 77 F., preferably 20 to 300 poises. The amounts of cis, trans and vinyl unsaturation are expressed in terms of the total unsaturation present in the polymer. The microstructure of the polymer can be determined by infrared analysis and a suitable method for analysis is given in connection with the polymers employed in the examples presented later in this disclosure. Butadiene polymers of this type can be prepared by the same type of initiation described in connection with the formation of the acidic-containing polymers but using organo lithium initiators. The organo lithium initiators can produce low vinyl polymers and for this reason are preferred for the production of the acidic-containing polymer as well. In the recovery of the plasticizer there is no need to take the steps indicated for addition of terminal acidic groups onto the polymer. For example, after polymerization is complete the polymer can be recovered by the addition of anhydrous hydrogen chloride and isopropyl alcohol and after washing, the solvent removed by evaporation.

A preferred method for preparing this polymer is through the use of a monofunctional organo lithium initiator. Such an initiator is normally a hydrocarbon which contains a single lithium atom, such as methyllithium, n-butyllithium, n-decyllithium, phenyllithium, naphthyllithium, p-tolyllithium, cyclohexyllithium and the like. In the recovery of these polymers, as stated before, there is no need to replace the lithium atom with an acidic group although mono-functional polymers can be employed in the practice of our invention, as demonstrated in the examples.

In the preparation of the solid propellant the liquid polymers, the inorganic oxidizing salt and the polyfunctional coupling agent are mixed together and then the temperature of the mixture is increased so that reaction occurs between the acidic groups of the polymers and the functional groups of the coupling agent. In the preparation of binder from liquid polymer of this type the polymers and the aziridinyl compounds are placed in a suitable dispersant type mixer and thoroughly mixed for a period of l to 10 minutes. The oxidizer which is finely powdered to a size in the range of from 1 to microns is then added and mixing is continued. During the latter mixing step the temperature is gradually increased to a temperature between about to 300 F., preferably between about 150 and 200 F. The material at this stage is a viscous slush which is then poured into a rocket case or suitable mold. The filled mold is then placed in an oven and cured for 24 to 48 hours or more at temperatures in the range of about 150 to 200 F.

The total amount of curative used is preferably about stoichiometric to somewhat above stoichiometric, for example, about per cent of the stoichiometric amount of curative based upon the acid equivalents of the polymers. With polymers in the lower range of equivalents, amounts of curative up to per cent of stoichiometric can be readily employed and with polymers in the higher range of acid equivalents as low as 10 percent of the stoichiometric amount of curative is effective. When using the lower amounts of curative the excess carboxyl groups are useful in developing adherence to surfaces such as the rocket cases, oxidizer particles or to glass or ceramic surfaces.

The solid propellants of this invention can contain, in addition to the binder fuel, a powdered metal such as aluminum and various compounding ingredients commonly employed in making composite propellants, such as plasticizers, oxidation inhibitors, reinforcing agents, wetting agents, modifiers, vulcanizing agents, curing agents, accelerators, burning rate catalysts, and the like. Propellant compositions can be formed into a grain having any desired shape or geometry, such as grains of the internal, external or internal-external burning types. These grains can be molded as described and can be restricted with any suitable and well known restricting material such as rubber. Examples of other powdered metals which can be incorporated into the propellant include boron, magnesium, beryllium, and the like. Alloys can also be used such as the aluminum alloys of boron, magnesium, manganese, copper or the like. Silicon can be used and the term metal is used herein to include silicon.

The rocket propellants of this invention have in general the composition range as follows:

Preferably the propellant compositions contain from 80 to 86 weight per cent inorganic oxidizing salt and from 14 to 20 weight per cent binder. The binder includes both the acidic polymer and the low vinyl diene plasticizer. From l0 to 19 weight per cent of the propellant composition in this preferred formulation is the acidic polymer while the plasticizer comprises from 1 to 4 weight per cent of the propellant.

Various types of compounding ingredients including fillers such as carbon black and mineral fillers can be incorporated into the polymer prior to reaction of the polymer with the polyfunctional coupling agent. Where it is desired to closely control the burning rate of the propellant compositions suitable burning rate catalysts can be incorporated therein. These catalysts include materials such as ferrocyanides sold under various trade names, such as Prussian blue, Steel blue, Bronze blue, Turnbulls blue, Chinese blue, New blue, Antwerp blue, Mineral blue, Paris blue, Berlin blue, I-Iamburg blue, Williamson blue, and the like. Other useful burning rate catalysts include copper chromite, ammonium dichromate, potassium dichromate, sodium dichromate and the like.

The advantages of our invention are illustrated by the following examples. In these examples specific conditions and materials are presented as being typical and should not be construed to limit our invention unduly.

EXAMPLE I Butadiene in toluene solvent was polymerized at 122 F. using lithiumstilbene adduct as catalyst. When 100 per cent conversion was reached, the product was reacted with CO The carbonated solutions were waterclear and extremely viscous; upon setting for several hours the viscosity decreased. Several polymerization lots were blended to a product having a viscosity of 1228 poises at 77 F. and a carboxyl content of 1.09 per cent.

A rocket propellant was prepared from the product which had the following composition:

Weight Polymer 19.57 tri(2-methy1-l-aziridinyl)phosphine oxide 0.43 ammonium perchlorate(200 microns) 56.00 ammonium perchlorate (18 microns) 24.00

The ingredients were thoroughly mixed together at room temperature; the fluid mass was then transferred to a suitable mold and the temperature raised to, and maintained at 160 F. for 96 hours, which produced a cured product free of voids and other imperfections,

and exhibiting the properties shown in Table II.

EXAMPLE II Weight Polymer 17.82 Plasticizer 1.78 Tri(2-methy1l-aziridinyl)phosphine 0.40 oxide Ammonium perchlorate (200 microns) 56.00 Ammonium perchlorate (18 microns) 24.00

EXAMPLE III A polymer having a viscosity of l 160 poises at 77 F. and a carboxyl content of 1.18 per cent was prepared according to the method of Example I. A rocket propellant employing this polymer had the following composition:

Weight Polymer 19.57 Tri(2-methyl-l-aziridinyl)phosphine 0.43 oxide Ammonium perchlorate (200 microns) 56.00 Ammonium perchlorate (18 microns) 24.00

Weight Polymer 17.83 Plasticizer 1.78 Tri(2methyl-l-aziridinly)phosphine 0.39 oxide Ammonium perchlorate (200 microns) 56.00 Ammonium perchlorate (18 microns) 24.00

EXAMPLE v A polymer having a viscosity of 2076 poises, a vinyl content of 35 per cent and a carboxyl content of 0.735 per cent was prepared as follows:

The following recipe was mixed and reacted for two hours at 122 F.:

Toluene (solvent) Butadiene Lithium-dimethylbutadiene adduct 1200 parts by weight parts by weight 20 millimols The conversion was quantitative and the product was reacted with C0 The following propellant composition was prepared with this polymer:

Weight Polymer 19.73 Tri(Z-methyl-l-aziridinyl)phosphine 0.27 oxide Ammonium perchlorate (200 microns) 56.00 Ammonium perchlorate (18 microns) 24.00

EXAMPLE VI A propellant having the following composition was prepared using the polymer of Example V and the plasticizer of Example 1V.

Weight Polymer 17.96 Plasticizer 1.79 Tri( 2-methyl- 1 -aziridinyl )phosphine 0.25 oxide Ammonium perchlorate (200 microns) 56.00 Ammonium perchlorate (18 microiTs) 24,00

EXAMPLE VII A polymer having a viscosity of 1104 poises, a vinyl content of 22 per cent and a carboxy content of 1.02

per cent (trans 37 per cent) was prepared from the following recipe at 122 F. with a reaction time of 1.5- hours. The polymerization product was reacted with CO Cyclohexane (solvent) 780 parts by weight viscosity of 580 poises at 77 F. The polymerization recipe was as follows:

1,3-Butadiene, parts by weight 100 P f 100 9 by weight Cyclohexane, parts by weight 1000 Lithium naphthalene 1methylbutad1ene 2O m1l|1mols Lithium mcthy|napmhalcne isoprene adduct initiator, millimoles l0 Tem 9 m 1 perature, F. 122 The followmg propellant was prepared w1th th1s poly- Time, hours 1.5 mer: Conversion quantitative Weight The initiator had been prepared by reacting isoprene, Polymer M63 15 methylnaphthalene (a commercial mixture of alphaiS Y yhp p and beta-methylnaphthalenes), and l1th1um 1n ether 2 Ammonium perchlorate (200 microns) 561,0 usmg the followmg proport1ons of 1ngred1ents. Ammonium perchlorate (18 microns) 24.00

Metnylnaphthalene, grams 14.2 (14.2 ml) 7 lsoprene, grams 6.6 (10.0 ml) EXAMPLE VIII 1 2O Lithium wire, grams 2.2 I l I Diethyl ether, ml A propellant havmg the following composltion was! prepared with the polymer of Example VII and the gg$ is plasticizer of Example IV.

.4 4 r w 2. To the reaction mixture was added 4 moles of butadiw h ene per mole of initiator to effect solubilization. The t amount of butadiene was calculated from the normality Polymer 15.76 of the reaction mixture which was determined by with- Plasticizer 3.94 Tmzmmhyb baziridinyhphosphine 030 I drawmg a sample and t1trat1ng1tw1th 0.1 N hydrochlo Oxide no ac1d. g i m ate (220 microns) 32.88 Immediately following the polymerization the unmmomum pm e mlcmns) quenched reaction mixture was carbonated using a T- i 7 i AT A TKBTIETI i Y Example Temperature, F. S," psi S, psi E,,,% E,,% Young's Modulus 1 170 88 80 86.0 91.8 165 (Control fOl 11) 75 139 133 83.8 91.5 285 40 574 539 24.4 37.7 5.642 1,466 1,165 2.8 4.1 66,693

111 170 88 70.5 75.5 204 (Control for W) 75 160 153 87.1 95.7 312 40 559 525 23.2 37.4 5,713 70 1,381 1,157 2.8 4.3 61,300

v 170 78 76 86.8 91.1 139 (Control for v1) 75 103 94.5 99.7 169 40 349 319 85.2 104.2 3,443 70 616 532 17.7 26.6 6,787

v11 121 107 35.5 45.0 676 (Control for VH1) 75 190 50.8 59.4 985 40 399 369 46.7 52.8 2.923 70 527 457 24.7 34.5 5.380

S, is the maximum tensile strength 5, is the tensile strength at break E is the elongation at maximum stress E, is the elongation at break tube. Carbon dioxide, under a pressure of 15-18 psig, and the polymer solution were fed into separate arms of the tube where they were mixed. The carbonated polymer solution was acidified with a hydrochloric acid-isopropyl alcohol mixture and washed with water until neutral. The major portion of the solvent was removed under vacuum and the remainder by purging with nitrogen. The resulting polymer had a carboxy content of 1.25 per cent and a vinyl content of 26.2 per cent.

Five separate plasticizers, A through E, were prepared as follows:

The polymerization recipe for plasticizers A and B was as follows:

l,3 Butadiene, parts by weight 100 Cyclohexane, parts by weight 780 n-Butyllithium, millimoles 40 Temperature, F. 122 Time, hours 4 Conversion quantitative 1,3-Butadiene, parts by weight 100 Cyclohexane, parts by weight 1000 n-Butyllithium, millimoles 40 Tetrahydrofuran, pans by weight 5 Temperature, "F. 86 Time, hours 1.5 Conversion quantitative Two runs were made as before and the polymer from th econd run was carbonated as hereinbefore described to form plasticizer D. Both products were recovered as described above.

The polymerization recipe for plasticizer E was as follows:

1,3-Butadiene, parts by weight 100 Toluene, parts by weight 800 Prefonned initiator, millimoles Temperature, F. 122 Time, hours 19 Conversion, 50

The preformed initiator was prepared by placing 2.02 grams (15.6 millimoles) of anhydrous nickel chloride (NiCl in a dry 7-ounce bottle which was then purged with nitrogen, capped, and 17 ml of an 0.82 molar solution of triethylaluminum in toluene 14 millimoles) was .added. The black slurry which formed was allowed to was removed over a steam bath under vacuum with a nitrogen ebullator.

Microstructures, carboxy contents, and viscosities (Brookfield viscosity at 77 F.) for the polymers from the foregoing runs were as follows:

Eighty parts by weight of the carboxy-telechelic polymer were blended with twenty parts of the liquid plasticizers. The polymers were blended with 250 phr finely ground, naturally occurring calcium carbonate (Whiting) and cured for 96 hours at 200 F. with 1.5 equivalents of tri(2-methyl-1-aziridinyl)phosphine oxide. The low temperature elongation of each specimen was determined and is shown in Table III. Two of the plasticizers, B and D were mono-functional, that is, contained carboxy groups on one end of the polymer molecule. Plasticizer B had a carboxy content of 1.28 per cent and plasticizer D had a carboxy content of 1.55 per cent. Plasticizers A, C and E were non-functional.

1 VI is a function of the degree of cure of the polymer and is the inverse swelling ratio of the polymer in n-heptane using the standard quick-swell" method, i.e., 3 hours at C. and then 3 hours at 30 C.

The above data demonstrate the unique effect which the liquid conjugated diene polymer having a micro structure in the specified range has upon the low temperature properties of the highly filled acidic polymer. This behavior of the low vinyl plasticizer in the Whiting filled stocks is indicative of similar behavior in more highly filled propellant compositions. In other words, the improvements demonstrated in low temperature properties by Examples 1 V111 can be expected only if the liquid diene plasticizer employed has a microstructure in the range specified.

Microstructures of the polymers in the above examples were determined by the infrared analysis according to the following procedure:

The polymer samples were dissolved in carbon disulfide so as to form a solution having 25 grams polymer per liter of solution. The infrared spectrum of each of the solutions (per cent transmission) was then determined in a commercial infrared spectrometer.

The per cent of the total unsaturation present as trans 1,4- was calculated according to the following equation and consistent units: 6 E/tc, where e extinction coefficient (liters-mols centimeters E extinction (log l /l); t path length (centimeters); and c concentration (mols double bond/liter). The extinction was determined at the 10.35 micron band and the extinction coefficient was 146 (liters-mols" centimeters The per cent of the total unsaturation present as 1,2- (or vinyl) was calculated according to the above equation, using the l 1.0 micron band and an extinction coefficient of 209 (liters-mols centimeters"). The cis l,4-unsaturation was determined by difference.

As will be apparent to those skilled in the art various modifications can be made in our invention without departing from the spirit or scope thereof.

We claim:

1. A solid propellant composition comprising an inorganic oxidizing salt and a synthetic polymeric binder formed by reacting a first uncured liquid polymer of conjugated dienes having four to 12 carbon atoms per molecule, said first polymer containing at least about two acidic groups per molecule with a polyfunctional organic compound containing at least 3 functional groups reactive with said acidic groups and selected from the group consisting of aliphatic polyepoxides, polyaziridinyl triazines, polyaziridinyl triphosphatriazines, triaziridinyl phosphine oxides, and triaziridinyl phosphine sulfides, said binder containing a plasticizing amount of a second liquid polymer of 1,3-butadiene having its unsaturation in the form of vinyl content in the range of to 25 per cent, trans content in the range of 0 to 60 per cent, and cis content in the range of 30- to 85 percent, and a viscosity in the range of 10 to 500 poises at 77 F.

2. The composition of claim 1 wherein said first polymer contains at least 2 terminally positioned acidic groups per molecule.

3. The composition of claim 1 wherein said first polymer is a copolymer of a conjugated diene with an unsaturated carboxylic acid having a maximum of 36 carbon atoms, from one to five double bonds, and from one to two carboxy groups.

4. A solid propellant composition comprising about 62 to 92 weight per cent inorganic oxidizing salt, 0 to 30 weight per cent powdered metal and 8 to 25 weight per cent synthetic polymeric binder formed by reacting a first uncured liquid polymer of a conjugated diene having four to eight carbon atoms per molecule with a polyaziridinyl compound containing at least two aziridinyl radicals per molecule, said aziridinyl radicals having the formula wherein the Rs are radicals containing up to a total of 20 carbon atoms per aziridinyl group, each R being selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl radicals and composites thereof, said first polymer containing at least about 2 terminal carboxy groups per molecule and having a viscosity in the range of 200 to 5000 poises at 77 F said binder containing a plasticizing amount of a second liquid polymer of l,3-butadiene, said sec- 10 80 to 86 weight per cent ammonium perchlorate and about 14 to 20 weight per cent polymeric binder formed by reacting a triaziridinyl compound having the formula wherein X is selected from the group consisting of oxygen and sulfur, P is phosphorous, and the Rs are radicals containing up to a total of 20 carbon atoms per aziridinyl group, each R being selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl radicals and composites thereof with a mixture of a first polymer of 1,3-butadiene having about 2 terminal carboxy groups per molecule and a viscosity at 77 F. in the range of 500 to 3000 poises and a second homopolymer of 1,3-butadiene having its unsaturation in the form of 0 to 15 per cent vinyl, O to 55 per cent trans, and 35 to per cent cis, and a viscosity at 77 F. in the range of 20 to 300 poises, said first polymer making up 10 to 19 weight per cent of said composition and said second polymer making up l to 4 weight per cent of said composition.

7. The composition of claim 6 wherein said triaziridinyl compound is tri(2-methyl-1-aziridinyl)phosphine oxide and said first polymer is polybutadiene.

8. A method of preparing a solid propellant composition which comprises forming a mixture of an inorganic oxidizing salt, a first liquid polymer of conjugated dienes having four to 12 carbon atoms per molecule, said first polymer containing at least about two acidic groups per molecule and a plasticizing amount of a second liquid polymer of 1,3-butadiene having its unsaturation in the form of 0 to 15 per cent vinyl, 0 to 55 per cent trans, and 35 to 85 per cent cis, and a viscosity in the range of 10 to 500 poises at 77 F., and curing said mixture by reacting acidic groups on said first polymer with a polyfunctional organic compound selected from the group consisting of aliphatic polyepoxides, polyaziridinyl triazines, polyaziridinyl triphosphatriazines, triaziridinyl phosphine oxides, and triaziridinyl phosphine sulfides.

9. A method of forming parts by weight of a solid propellant composition which comprises mixing about 62 to 92 parts of inorganic oxidizing salt, 0 to 30 parts of powdered metal, 7 to 24 parts of a first polymer of conjugated diene containing four to eight carbon atoms per molecule, said first polymer having about two terminal carboxy groups per molecule and a viscosity in the range of 200 to 5000 poises at 77 F., and l to 18 parts of a second polymer of 1,3-butadiene, said second polymer having its unsaturation in the form of 0 to l5 per cent vinyl, to 55 per cent trans, and 35 to 85 per cent cis, and a viscosity in the range of 20 to 300 poises at 77 F., and curing the resulting mixture by reacting said first polymer with a polyaziridinyl compound containing at least two aziridinyl radicals per molecule, said aziridinyl radicals having the fonnula n as N wherein the Rs are radicals containing up to a total of 20 carbon atoms per aziridinyl group, each R 0 ene and said aziridinyl compound is tri(2-methyl-laziridinyl )phosphine oxide.

12. The method of claim 10 wherein the mixture of salt and liquid polymer is poured as a slush into a rocket case and cured in situ. 

1. A SOLID PORPELLANT COMPOSITION COMPRISING AN INORGANIC OXIDIZING SALT AND A SYNTHETIC POLYMERIC BINDER FORMED BY REACTING A FIRST UNCURED LIQUID POLYMER OF CONJUGATED DIENES HAVING FOUR TO 12 CARBON ATOMS PER MOLECULE, SAID FIRST POLYMER CONTAINING AT LEAST ABOUT TWO ACIDIC GROUPS PER MOLECULE WITH A POLYFUNCTIONAL ORGANIC COMPOUND CONTAINING AT LEAST 3 FUNCTIONAL GROUPS REACTIVE WITH SAID ACIDIC GROUPS AND SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC POLYEPOXIDES, POLYAZIRIDINYL TRIAZINES, POLYAZIRIDINYL TRIPHOSPHATRIAZINES, TRIAZIRIDINYL PHOSPHOSE OXIDES AND TRIAZIRIDINYL PHOSPHINE SULFIDES, SAID BINDER CONTAINING A PLASTICIZUING AMOUNT OF A SECOND LIQUID CONTAINING A HAVING ITS UNSATURATION IN THE FORM OF VINYL CONTENT IN THE RANGE OF 0 TO 25 PER CENT, TRANS CONTENT IN THE RANGE OF 0 TO 60 PER CENT, AND CIS CONTENT IN THE RANGE OF 30 TO 84 PER CENT, AND A VISCOSITY IN THE RANGE OF 10 TO 500 POISES AT 77*F. THE APPARATUS CONSISTS OF A PLURALITY OF LONGITUDINALLY SPACED WORK STATIONS THROUGH WHICH THE WORK IS SUCCESSIVELY MOVED FOR PROGESSIVELY SHAPING AND ADHERING THE PLASTIC LAMINATE TO THE WORK, SUCH WORK BEING GUIDED THROUGH THE APPARATUS BY RECEIPT OF A DOWNWARDLY PROJECTING PORTION FROM THE WORK IN A GUIDE TRACK EXTENDING THE ENTIRE LENGHT OF THE APPARATUS. A BACK DIE BENDS THE LAMINATE TO COMFORM TO THE GENERAL SHAPE OF THE BACKSPLASH AND COUNTERTOP AFTER HEATING, A FINGERS AND PRESSURE ROLLS ARE USED TO PROGRESSIVELY BEND AND PRESS THE PROJECTING EDGES OF THE LAMINATE INTO FIRM CONTACT WITH THE EDGES OF THE COUNTERTOP AND BACKSPLASH. FLOATING CUTTERS ARE ALSO USED TO TRIM THE EXCESS LAMINATE MATERIAL EXTENDING BEYOMD THE COUNTERTOP AND BACKSPLASH EDGES, AND SUCH EXCESS MATERIAL MAY BE PICKED UP BY A SUCTION BLOWER OR REMOVED BY A ROTARY BRUSH PRIOR TO PASSAGE THROUGH FINAL PRESSURE ROLLS.
 2. The composition of claim 1 wherein said first polymer contains at least 2 terminally positioned acidic groups per molecule.
 3. The composition of claim 1 wherein said first polymer is a copolymer of a conjugated diene with an unsaturated carboxylic acid having a maximum of 36 carbon atoms, from one to five double bonds, and from one to two carboxy groups.
 4. A solid propellant composition comprising about 62 to 92 weight per cent inorganic oxidizing salt, 0 to 30 weight per cent powdered metal and 8 to 25 weight per cent synthetIc polymeric binder formed by reacting a first uncured liquid polymer of a conjugated diene having four to eight carbon atoms per molecule with a polyaziridinyl compound containing at least two aziridinyl radicals per molecule, said aziridinyl radicals having the formula
 5. The composition of claim 4 wherein said first polymer makes up about 7 to 24 weight per cent of said composition and said second polymer makes up about 1 to 18 weight per cent of said composition.
 6. A solid propellant composition comprising about 80 to 86 weight per cent ammonium perchlorate and about 14 to 20 weight per cent polymeric binder formed by reacting a triaziridinyl compound having the formula
 7. The composition of claim 6 wherein said triaziridinyl compound is tri(2-methyl-1-aziridinyl)phosphine oxide and said first polymer is polybutadiene.
 8. A method of preparing a solid propellant composition which comprises forming a mixture of an inorganic oxidizing salt, a first liquid polymer of conjugated dienes having four to 12 carbon atoms per molecule, said first polymer containing at least about two acidic groups per molecule and a plasticizing amount of a second liquid polymer of 1,3-butadiene having its unsaturation in the form of 0 to 15 per cent vinyl, 0 to 55 per cent trans, and 35 to 85 per cent cis, and a viscosity in the range of 10 to 500 poises at 77* F., and curing said mixture by reacting acidic groups on said first polymer with a polyfunctional organic compound selected from the group consisting of aliphatic polyepoxides, polyaziridinyl triazines, polyaziridinyl triphosphatriazines, triaziridinyl phosphine oxides, and triaziridinyl phosphine sulfides.
 9. A method of forming 100 parts by weight of a solid propellant composition which comprises mixing about 62 to 92 parts of inorganic oxidizing salt, 0 to 30 parts of powdered metal, 7 to 24 parts of a first polymer of conjugated diene containing four to eight carbon atoms per molecule, said first polymer having about two terminal carboxy groups per molecule and a viscosity in the range of 200 to 5000 poises at 77* F., and 1 to 18 parts of a second polymer of 1,3-butadiene, said second polymer having its unsaturation in the form of 0 to 15 per cent vinyl, 0 to 55 per cent trans, and 35 to 85 per cent cis, and a viscosity in the range of 20 to 300 poises at 77* F., and curing the resulting mixture by reacting said first polymer with a polyaziridinyl compound containing at least two aziridinyl radicals per molecule, said aziridinyl radicals having the formula
 10. The method of claim 9 wherein 80 to 86 parts of said salt are mixed with 10 to 19 parts of said first polymer and one to four parts of said second polymer.
 11. The method of claim 10 wherein said salt is ammonium perchlorate, said first polymer is polybutadiene and said aziridinyl compound is tri(2-methyl-1-aziridinyl)phosphine oxide.
 12. The method of claim 10 wherein the mixture of salt and liquid polymer is poured as a slush into a rocket case and cured in situ. 